Hydraulic braking systems for vehicles

ABSTRACT

A brake control unit for incorporation between an hydraulic master cylinder and a wheel brake actuator comprising an inertiacontrolled valve member which is movable into engagement with a seating to cut-off communication between an inlet for connection to the master cylinder and an outlet for connection to the hydraulic actuator when the deceleration of the vehicle in which the unit is incorporated exceeds a predetermined value. The valve seating is movable between a first inoperative retracted position and a second operative advanced position, and means are incorporated for preventing the valve member from engagement with the seating unless the seating is in the advanced position.

Unite States atent [191 [ll] 3,727,990 Vogt 5] Apr. 17, 1973 s4HYDRAULIC BRAKING SYSTEMS FOR 3,476.44} 1 H1969 Bratten ..1ss/349 xVEHICLES [75] Inventor: Hans Josef Vogt, Vallendar, Germany [73]Assignee: Girling Limited, Birmingham, En-

gland [22] Filed: Mar. 1, 1972 [21] Appl. N0.: 230,750

[30] Foreign Application Priority Data Mar. l9, l97l Great Britain..7.445/7l [52] US. Cl ..303/6 C, 137/38, 303/24 [51] Int. Cl. ..B60t8/14 [58] Field of Search ..303/24, 6 C; 137/38; 188/349 [56] ReferencesCited UNITED STATES PATENTS 3,398.757 8/1968 Milster 303/6 C PrimaryExaminer-Richard A. Schacher Attorney-Samuel Scrivener, Jr. et al.

[57] ABSTRACT A brake control unit for incorporation between anhydraulic master cylinder and a wheel brake actuator comprising aninertia-controlled valve member which is movable into engagement with aseating to cut-off communication between an inlet for connection to themaster cylinder and an outlet for connection to the hydraulic actuatorwhen the deceleration of the vehicle in which the unit is incorporatedexceeds a predetermined value.'The valve seating is movable between afirst inoperative retracted position and a second operative advancedposition, and means are incorporated for preventing the valve memberfrom engagement with the seating unless the seating is in the advancedposition.

6 Claims, 1 Drawing Figure HYDRAULIC BRAKING SYSTEMS FOR VEHICLESSPECIFIC DESCRIPTION This invention relates to a new or improved brakecontrol unit for incorporation between a master cylinder and anhydraulic actuator of a wheel brake in an hydraulic braking system for avehicle, the control unit being of the kind comprising aninertia-controlled valve member which is movable into engagement with aseating to cutoff communication between an inlet for connection to themaster cylinder and an outlet for connection to the hydraulic actuatorwhen the deceleration of the vehicle in which the unit is incor poratedexceeds a predetermined value.

In a braking system incorporating a brake control unit of the kind setforth when the vehicle is subjected to an excessive deceleration or whenthe control unit is tilted excessively due to deflections of thesuspension of the vehicle there is a tendency for the valve member toengage with the seating to cut-off the supply of pressure fluid to thehydraulic actuator at least before a minimum braking pressure has beenapplied to the hydraulic actuator.

According to our invention in a brake control unit of the kind set forththe valve seating is movable between a first inoperative retractedposition and a second operative advanced position, and means areincorporated for preventing the valve member engaging with the seatingunless the seating is in the advanced position.

The seating is moved into the advanced position only after at least aminimum braking pressure has been applied to the outlet.

Conveniently a differential piston works in a complementary stepped borein a housing and the seating surrounds a longitudinally extending borein the piston and is located in the end of the piston which is ofsmaller area, the valve member being movable within a chamber incommunication with the smaller end of the stepped bore and a stop beingprovided in the housing at a position to prevent the valve member fromengaging with the seating unless the seating is disposed in the advancedposition adjacent to the stop.

A spring normally acts on the differential piston to hold it in aretracted position towards the larger end of the bore with the seatingspaced from the stop. When opposite ends of the piston are subjected toequal pressures, due to the differential areas of the ends of thepiston, the piston is moved towards the smaller end of the bore to urgethe seating into engagement with the valve member. Thus communicationbetween the inlet and the outlet is cut-off.

The value of the pressure to which the piston is subjected to move itinto the operative position is chosen to ensure that at least a minimumpressure is supplied to the hydraulic actuator before the seating canengage with the valve member. Thus the operation ofthe brake controlunit is unaffected by excessive vehicle decelerations or suspensiondeflections.

One embodiment of our invention is illustrated in the accompanyingdrawing which is a longitudinal section through a brake control unit inaccordance with our invention.

In the control valve illustrated in the accompanying drawings 1 is ahousing which is constructed from complementary housing parts 2 and 3 ofwhich adjacent end faces 4 and 5 are clamped together. The housing part2 is provided with a longitudinal bore 6 which extends inwardly from itsinner end, and the bore 6 is counter-bored at 7 to receive an annularsleeve 8 of an internal diameter less than that of the bore 6. Theinternal surface of the sleeve 8 and the bore 6 define a stepped bore 9in which works a differential piston 10. The differential piston 10 isnormally urged towards a stop 11 at the closed outer end of the housingpart 2 by means of a compression spring 13 acting. between the portionof the piston 10 which is of greater diameter and the adjacent end ofthe sleeve 8.

The housing part 3 is provided with a longitudinal bore 14 concentricwith and of a diameter substantially equal to that of the counterbore 7.

The sleeve 8 is of an axial length slightly less than that of thecounterbore 7 and is preferably clamped against a shoulder 15 in thehousing part 2 at a step in the change in diameter between the bore 6and the counterbore 7 by means of a stop member 16. The stop member 16comprises an axially extending collar 17 formed at an intermediate pointin its length with an outwardly directed radial flange 18 which isclamped between, and in sealing engagement with, the adjacent end facesof the housing parts 2 and 3, and an inwardly directed radial flange 20which engages with the outer end of the sleeve 8 to clamp the sleeve 8against the shoulder 15. The internal diameter of the flange 20 issubstantially equal to that of the sleeve 8.

A sleeve 21 is carried by or is integral with the end face of the collar18 remote from the sleeve 8 and extends axially into the bore 14 in thehousing part 3. A series of circumferentially spaced ribs 22 formed inthe internal face of the sleeve 21 define tracks between which is guidedan inertiacontrolled valve member in the form of a ball 23 locatedwithin the bore 14 which defines a chamber. The ball 23 is movable inthe chamber 14 on the tracks 22 through an axial distance between thestop member 16 and a stop 24 at the closed end of the housing part 3. Asillustrated, the innermost end of the face of the flange 20 remote fromthe sleeve 8 is of discontinuous arcuate outline concentric with andequal in diameter to that of the ball 23 to form a stop face 25 withwhich the ball 23 is adapted to engage. Gaps in the stop face 25 providepassages for fluid when the ball is in engagement with the stop face.

The closed outer end of the housing part 3 is formed with a radialpassage 26 communicating with the bore 14, and the closed outer end ofthe housing part 2 is formed with a radial passage 27. Normally thepassages 26 and 27 are in communication through a longitudinallyextending axial bore 28 in the piston 10, and a valve seating 29surrounding the bore 28 is provided at the inner end of the piston 10which is of smaller diameter.

The brake control unit is mounted in a vehicle'in an inclined positionwith the closed end of the housing portion 11 at the forward end. Thepassage 27 is connected to hydraulic actuators of wheel brakes, normallythe brakes on the rear wheels of the vehicle.

In the normal off position of brakes the components of the control unitassume the positions shown in the drawings with the ball 23 spaced fromthe seating 29 and resting against the stop 24 under the influence ofgravity, and the differential piston 10 urged into engagement with thestop 1 1 by the force in the spring 1-3.

When the master cylinder is operated to apply the brakes and thedeceleration of the vehicle is below a predetermined value required tocause the'ball 23 to engage with the seating 29, fluid under pressure isdelivered to the brake actuators through the chamber 14, the axial bore28 in the piston 10, the bore 6, and the outlet passage 27. At the sametime the master cylinder pressure is acting on the smaller end of thedifferential piston and the pressure applied to the brakes is acting onthe larger end. So long as the ball 23 does not engage with the seating29 these pressures are equal. Owing to the differential areas of the twoends of the piston 10, the piston 10 is moved progressively towards thesmaller end of the stepped bore in response to increases in pressure andagainst the action of the spring 13 in which energy is stored until thesmaller end of the piston 10 is substantially aligned with the stop face25. When this occurs a predetermined minimum pressure is applied to theoutlet passage 27.

When the deceleration of the vehicle exceeds the predetermined value theball 23 moves into engagement with the seating 29 and cuts off directcommunication between the master cylinder and the brake actuators, atthe same time engaging with, or being placed in close proximity to, thestop face 25.

Any increase in the pressure of the fluid supplied by the mastercylinder then acts on the smaller end of the differential piston 10 and,with the assistance of the spring 13, moves the piston 10 towards thelarger end of the stepped bore 9 against the pressure already existingin the larger end of the bore 9 which is the pressure applied to thehydraulic actuators. During this movement of the piston 10 the ball isin engagement, or engages, with the stop face 25. Thus the valve seating29 moves out of engagement with the ball 23 so that the increased mastercylinder pressure is applied to the brake actuators through the axialbore 28 in the piston 10 and the rear wheel brakes are re-appliedautomatically.

The increased pressure applied to the brakes also acts on the oppositeend of the differential piston 10 and, owing to the differential areasof the two ends of the piston 10, causes the piston 10 to move towardsthe smaller end of the stepped bore 9 with the result that the seating29 engages with the ball 23 to cut-off again the supply of pressurefluid to the brake actuators.

The sequence of operations described above is repeated automaticallyupon each successive increase in master cylinder pressure during any onebrake application, and each successive rel-application of the rear wheelbrakes takes place at a progressively increased pressure.

The ball 23 may move towards the seating 29 under the influence offorces other than those produced when the deceleration of the vehicle,in response to a brake application, exceeds a predetermined value. Forexample the ball 23 may move towards the seating 29 when the controlunit is tilted excessively due to deflections of the suspension of thevehicle in which it is installed. Alternatively the ball 23 may movetowards the seating 29 due to the impingement on the ball 23 of highpressure fluid when the master cylinder is operated rapidly. in eitherof these cases movement of the ball 23 towards the seating 29 isarrested by the provision of the stop face 25 which prevents the ball 29from engaging with the seating 29 which, at that time, is disposed inthe retracted position shown in the drawings by the force in the spring13 holding the differential piston 10 against the stop at the closed endof the stepped bore 9.

When the ball 23 engages with the stop face 25 due to the influence ofsuspension movements when the brake is applied by operation of themaster sylinder, fluid under pressure passes to the brake actuators ofthe rear wheel brakes through the axial bore 28 in the piston 10. Thebrakes are applied until the hydraulic pressures which acts on oppositeends of the differential piston 10 attains a value sufficient to applyto the piston 10, due to the differential areas of the ends of thepiston 10, a force of a magnitude-sufficient to move the piston 10towards the smaller end of the stepped bore 9 and urge the seating 29into engagement with the ball 23. The supply of fluid to the brakeactuators is thus cut-off. Any subsequent increase in the applied fluidpressure from the master cylinder applied to the smaller end of thepiston 10 serves to reapply the brakes in successive stages as describedabove.

Should the ball 23 move towards the seating 29 due to theefiect of highpressure fluid from the master cylinder, such high pressure fluid issupplied to that brake actuators through the axial bore 28 until thatpressure attains a value sufficient to cause the differential piston 10to move towards the smaller end of the stepped bore 9 so that theseating 29 engages with the ball 23 to cut off the supply of pressurefluid to the actuators of the rear brakes. Thereafter re-application ofthe brakes in response to further increase in master cylinder pressuretakes place as described above.

The value of the pressure at which the seating 29 is operative to engagewith the ball 23 is chosen to be consistent with subjecting the vehicleto the said predetermined value of deceleration at which the ball 23would normally be urged towards the seating 29 under the influence ofinertial forces.

lclaim: v

l. A brake control unit for incorporation between a master cylinder andan hydraulic actuator of a wheel brake in an hydraulic braking system,said control unit comprising a housing having an inlet for connection toa master cylinder and an outlet for connection to an hydraulic actuator,a valve seating in said housing located between said inlet and saidoutlet, and an inertia-controlled valve member movable into engagementwith said seating to cut-off communication between said inlet and saidoutlet, when the deceleration of a vehicle in which said unit isincorporated exceeds a predetermined value, wherein said valve seatingis movable between a first inoperative retracted position and a secondoperative advanced position, and means are incorporated for preventingsaid valve member from engaging with said seating unless said seating isin said advanced position.

2. A brake control unit as claimed in claim 1, wherein said housingincorporates a stepped bore, and a differential piston works in saidstepped bore and is provided with a longitudinally extending bore, andwherein said seating is located in an end of said piston which is ofsmaller area, and means are incorporated to define a chamber in saidhousing in communication with an end of said stepped bore which is ofsmaller area, said valve member being movable within said chamber, and astop being provided in said housing at a position to prevent said valvemember from engaging with said seating unless said seating is disposedin said advanced position adjacent to said stop.

3. A brake control unit as claimed in claim 2, wherein said stopcomprises a stop face in said housing at said smaller area end of saidstepped bore.

4. A brake control unit as claimed in claim 3, wherein saidinertia-controlled valve member comprises a ball, and said stop face isof arcuate outline concentric with and equal in diameter to that of saidball.

5. A brake control unit as claimed in claim 3,

wherein said stop face is provided within gaps defining passages forfluid from said inlet to act on said end of said piston which is ofsmaller area when said inertiacontrolled valve member is in engagementwith said stop face.

6. A brake control unit as claimed in claim 2, wherein a spring normallyacts on said differential piston to hold it in a retracted positiontowards an end of said bore which is of greater area with said seatingpositioned in said first inoperative position in which said seating isspaced from said stop.

1. A brake control unit for incorporation between a master cylinder and an hydraulic actuator of a wheel brake in an hydraulic braking system, said control unit comprising a housing having an inlet for connection to a master cylinder and an outlet for connection to an hydraulic actuator, a valve seating in said housing located between said inlet and said outlet, and an inertia-controlled valve member movable into engagement with said seating to cut-off communication between said inlet and said outlet, when the deceleration of a vehicle in which said unit is incorporated exceeds a predetermined value, wherein said valve seating is movable between a first inoperative retracted position and a second operative advanced position, and means are incorporated for preventing said valve member from engaging with said seating unless said seating is in said advanced position.
 2. A brake control unit as claimed in claim 1, wherein said housing incorporates a stepped bore, and a differential piston works in said stepped bore and is provided with a longitudinally extending bore, and wherein said seating is located in an end of said piston which is of smaller area, and means are incorporated to define a chamber in said housing in communication with an end of said stepped bore which is of smaller area, said valve member being movable within said chamber, and a stop being provided in said housing at a position to prevent said valve member from engaging with said seating unless said seating is disposed in said advanced position adjacent to said stop.
 3. A brake control unit as claimed in claim 2, wherein said stop comprises a stop face in said housing at said smaller area end of said stepped bore.
 4. A brake control unit as claimed in claim 3, wherein said inertia-controlled valve member comprises a ball, and said stop face is of arcuate outline concentric with and equal in diameter to that of said ball.
 5. A brake control unit as claimed in claim 3, wherein said stop face is provided within gaps defining passages for fluid from said inlet to act on said end of said piston which is of smaller area when said inertia-controlled valve member is in engagement with said stop face.
 6. A brake control unit as claimed in claim 2, wherein a spring normally acts on said differential piston to hold it in a retracted position towards an end of said bore which is of greater area with said seating positioned in said first inoperative position in which said seating is spaced from said stop. 